Generally, swaging is processing for forming an enlarged diameter portion at a prescribed portion of a raw material by pressing the raw material in the axial direction thereof. In the swaging processing, if the raw material is budded during the swaging processing, the obtained product becomes poor in shape (wrinkled or laps), deteriorating the value as a product. In order to prevent the occurrence of such buckling, conventionally, the following swaging method is known (see Japanese Unexamined Laid-open Patent Publication No. S48-62646, pages 1-2, FIGS. 1-4).
In this method, a pressing die is fitted in a forming dented portion of a female die, and a raw material is inserted in the forming dented portion via a penetrated hole formed in the pressing die. Then, a male die is inserted in the penetrated hole to forcibly press the raw material toward the forming dented portion to thereby fill the forming dented portion with the raw material while moving the pressing die backward to obtain a product having a prescribed shape.
According to the aforementioned conventional processing method, the peripheral surface of the raw material pressed in the forming dented portion of the female die is restrained by the female die during the processing. Accordingly, the conventional processing method can be classified into a restrain swaging method. The restrain swaging method, however, has such a drawback that higher forming pressure is generally required. Thus, in the conventional processing method, it is required to prepare a forging apparatus capable of generating higher forming pressure, causing higher cost to employ such a forging apparatus. Furthermore, since larger load will be applied to the forming dented portion of the female die at the time of the swaging processing, resulting in a shortened life of the female die.
The description herein of advantages and disadvantages of various features, embodiments, methods, and apparatus disclosed in other publications is in no way intended to limit the present invention. Indeed, certain features of the invention may be capable of overcoming certain disadvantages, while still retaining some or all of the features, embodiments, methods, and apparatus disclosed therein.